drm/radeon: call hpd_irq_event on resume

commit dbb17a21 upstream.

Need to call this on resume if displays changes during
suspend in order to properly be notified of changes.
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/gpu/drm/radeon/radeon_device.c

@@ -960,6 +960,7 @@ int radeon_resume_kms(struct drm_device *dev)
 	}
 
 	drm_kms_helper_poll_enable(dev);
+	drm_helper_hpd_irq_event(dev);
 	return 0;
 }